sigwaitinfo() suspends execution of the calling thread until one of
the signals in set is pending (If one of the signals in set is
already pending for the calling thread, sigwaitinfo() will return
immediately.)
sigwaitinfo() removes the signal from the set of pending signals and
returns the signal number as its function result. If the info
argument is not NULL, then the buffer that it points to is used to
return a structure of type siginfo_t (see sigaction(2)) containing
information about the signal.
If multiple signals in set are pending for the caller, the signal
that is retrieved by sigwaitinfo() is determined according to the
usual ordering rules; see signal(7) for further details.
sigtimedwait() operates in exactly the same way as sigwaitinfo()
except that it has an additional argument, timeout, which specifies
the interval for which the thread is suspended waiting for a signal.
(This interval will be rounded up to the system clock granularity,
and kernel scheduling delays mean that the interval may overrun by a
small amount.) This argument is of the following type:
struct timespec {
long tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
}
If both fields of this structure are specified as 0, a poll is per‐
formed: sigtimedwait() returns immediately, either with information
about a signal that was pending for the caller, or with an error if
none of the signals in set was pending.

EAGAIN No signal in set was became pending within the timeout period
specified to sigtimedwait().
EINTR The wait was interrupted by a signal handler; see signal(7).
(This handler was for a signal other than one of those in
set.)
EINVAL timeout was invalid.

In normal usage, the calling program blocks the signals in set via a
prior call to sigprocmask(2) (so that the default disposition for
these signals does not occur if they become pending between
successive calls to sigwaitinfo() or sigtimedwait()) and does not
establish handlers for these signals. In a multithreaded program,
the signal should be blocked in all threads, in order to prevent the
signal being treated according to its default disposition in a thread
other than the one calling sigwaitinfo() or sigtimedwait()).
The set of signals that is pending for a given thread is the union of
the set of signals that is pending specifically for that thread and
the set of signals that is pending for the process as a whole (see
signal(7)).
Attempts to wait for SIGKILL and SIGSTOP are silently ignored.
If multiple threads of a process are blocked waiting for the same
signal(s) in sigwaitinfo() or sigtimedwait(), then exactly one of the
threads will actually receive the signal if it becomes pending for
the process as a whole; which of the threads receives the signal is
indeterminate.
sigwaitinfo() or sigtimedwait(), can't be used to receive signals
that are synchronously generated, such as the SIGSEGV signal that
results from accessing an invalid memory address or the SIGFPE signal
that results from an arithmetic error. Such signals can be caught
only via signal handler.
POSIX leaves the meaning of a NULL value for the timeout argument of
sigtimedwait() unspecified, permitting the possibility that this has
the same meaning as a call to sigwaitinfo(), and indeed this is what
is done on Linux.
C library/kernel differences
On Linux, sigwaitinfo() is a library function implemented on top of
sigtimedwait().
The glibc wrapper functions for sigwaitinfo() and sigtimedwait()
silently ignore attempts to wait for the two real-time signals that
are used internally by the NPTL threading implementation. See
nptl(7) for details.
The original Linux system call was named sigtimedwait(). However,
with the addition of real-time signals in Linux 2.2, the fixed-size,
32-bit sigset_t type supported by that system call was no longer fit
for purpose. Consequently, a new system call, rt_sigtimedwait(), was
added to support an enlarged sigset_t type. The new system call
takes a fourth argument, size_t sigsetsize, which specifies the size
in bytes of the signal set in set. This argument is currently
required to have the value sizeof(sigset_t) (or the error EINVAL
results). The glibc sigtimedwait() wrapper function hides these
details from us, transparently calling rt_sigtimedwait() when the
kernel provides it.

This page is part of release 5.01 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 SIGWAITINFO(2)